What happens if only one squad is filled out? That's a lot of people to expect.
Also, not to nitpick, but I'd recommend you use a different term than "fireteam" for this force, because in military terminology, a fireteam is a small number of troops (4+), which when paired (Army) or tripled (Marines) together, make a squad.

Following UNSC organization, you could call it a "[url=http://halo.wikia.com/wiki/UNSC_Military_Organization]combat team[/url]," which is two squads totalling 16-24 men in all. But I really doubt you'll have that many people and a single squad may be more realistic. I'm also of the opinion that anything above E-6 is a rather high rank for this composition.